The present invention relates to a rolling bearing and a bearing apparatus. More particularly, the present invention relates to a rolling bearing and a bearing apparatus for use in office appliances such as copying machine and laser beam printer.
A rolling bearing for office appliances such as copying machine and laser beam printer is normally mounted in a housing made of resin for use. As the lubricant for such a rolling bearing there is normally used a grease taking into account maintenance and other requirements.
Referring to the type of grease to be used for such a rolling bearing, a grease comprising as a base oil silicone oil or fluorine oil is used for sites to be exposed to extremely high temperature such as fixing roller in copying machine or laser beam printer. For other sites, a grease comprising as a base oil a mineral oil, which is inexpensive and widely used, or synthetic oil except silicone oil and fluorine oil is normally used.
A technique for preventing the grease packed in the interior of the bearing from leaking out of the bearing has been already proposed (JP-A-2-78069 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d)). Further, a technique for preventing the grease from leaking out of the bearing as well as improving the lubricating properties of the grease in the interior of the bearing has been already proposed (JP-A-10-326468).
In this kind of rolling bearing, a rust preventive solution is applied to the entire surface of the bearing rings (inner ring and outer ring) to form a rust preventive film on the surface of the bearing. In this arrangement, the rolling bearing is rendered rustproof during the storage in a single form until mounting to the office appliances or in a high temperature and humidity atmosphere during the transportation of the office appliances.
In other words, it has been heretofore practiced to apply a rust preventive solution comprising a rust preventive diluted with a diluent to the entire surface of the rolling bearing so that the rolling bearing is rendered rustproof.
Since the resin material from which the housing is made is subject to load developed by residual stress from molding or external stress, the rise of the ambient temperature during operation causes the rust preventive solution attached to the outer surface of the outer ring and other sites to enter in the resin, possibly causing the deterioration of the strength of the resin. The deterioration of the strength of the resin causes the occurrence of crack or craze (hereinafter referred to as xe2x80x9ccrack or the likexe2x80x9d), resulting in the maloperation of office appliances. Therefore, the selection of the kind of rust preventive has heretofore been made taking into account its effect on the resin material.
As a rust preventive which causes the deterioration of the strength of resin there has heretofore been known a compound having a high polarity such as hydrocarbon compound containing oxygen as a hetero element in a molecular structure such as ester bond and ether bond (e.g., sorbitan fatty acid ester, alkylphosphoric acid and a salt thereof, polyoxyalkylene alkyl ether phosphoric acid and a salt thereof). On the other hand, such a rust preventive is diluted with a diluent comprising an ester-based, ether-based, glycol-based or alcohol-based lubricant or solvent in a concentration of from 0.5% to 10% by weight before use. Therefore, the deterioration of the strength of resin is attributed to the kind of the rust preventive used as well as to the effect of the diluent used.
Therefore, as a rust preventive for this purpose there has heretofore been normally used a metal salt of organic sulfonate free of compound or solvent having a high polarity. The concentration of the rust preventive is adjusted with a mineral oil or synthetic hydrocarbon oil as a diluent.
In recent years, a modified polyphenylene oxide (Noryl (R)) having an excellent heat resistance and dimensional stability which is available at a relatively low price has been used as a resin material from which a housing is made in the art of information electronic apparatus. However, such a modified polyphenylene oxide has a low bending strength and thus is occurred to crack or the like due to strain even if a slight amount of rust preventive is attached thereto. Therefore, in the case where a housing made of modified polyphenylene oxide is used, the bearing is wiped to remove the rust preventive left on the exterior of the bearing before mounted to the office appliances.
The foregoing rust preventive solution containing a metal salt of organic sulfonate has an affinity for general-purpose grease and thus can be easily attached to the entire surface of the bearing. However, this rust preventive solution is disadvantageous in that it can enter in the resin material to deteriorate the strength of the resin and thus leaves something to be desired with respect to such a resin material having a low crystallinity.
In other words, the resin housing in which the rolling bearing is mounted is made of various resin materials depending on the purpose. However, when the housing is formed by a resin material having a low crystallinity, it is disadvantageous in that the rust preventive solution can enter in the resin material to deteriorate the strength of the resin, resulting in the occurrence of crack or the like on the housing.
On the other hand, the above-described JP-A-2-78069 and JP-A-10-326468 disclose a technique for preventing the grease from leaking out of the bearing. However, there are no countermeasures against the entrance of a rust preventive containing a diluent into the resin material.
Further, the foregoing approach involving the use of a modified polyphenylene oxide as a resin material is disadvantageous in that the exterior of the bearing is subject to rusting that causes the deterioration of the bearing life because the rust preventive attached to the exterior of the bearing is removed before the mounting of the rolling bearing in the housing as mentioned above.
It is therefore an object of the invention to provide a rolling bearing and a bearing apparatus which each can be secured with desired rustproofness without deteriorating the strength of various resin materials.
The foregoing object of the present invention will become apparent from the following detailed description and examples.
As mentioned above, the deterioration of the strength of resin is presumably attributed to the fact that the rust preventive solution prepared by adding a rust preventive to a diluent enters in the resin material.
Under these circumstances, the inventors made extensive studies of rust preventive solution which can hardly enter in the resin material. As a result, a knowledge was obtained that a rust preventive solution containing an oil-repellent rust preventive such as fluorine-based rust preventive has a low affinity for resin materials and thus can hardly enter in resin materials, making it possible to prevent the deterioration of the strength thereof. Another knowledge was obtained that since such an oil-repellent rust preventive has no compatibility with water or a hydrocarbon compound, it cannot deteriorate the strength of resin materials containing a hydrophilic group as well.
The present invention has been worked out on the basis of this knowledge. More specifically, the problems are resolved by the following Embodiments (1) to (18):
(1) A rolling bearing which comprises an inner ring fitted onto a shaft, an outer ring fitted in the housing, a plurality of rolling elements provided interposed between the inner ring and the outer ring and a lubricant packed thereinside and which is mounted between the shaft and the housing, wherein a rust preventive film comprising an oil-repellent material is formed on at least the outer surface of the outer ring and the inner surface of the inner ring.
(2) The rolling bearing as described in (1), wherein at least one of the shaft and the housing is formed by a resin material.
(3) The rolling bearing as described in (1), wherein the rust preventive film is formed by applying a rust preventive solution having from 0.5% to 10% by weight of a fluorine-based rust preventive dissolved in a fluorine-based diluent.
(4) The rolling bearing as described in (3), wherein the fluorine-based rust preventive is a single material comprising a molecular structure comprising a main chain substituted by fluorine which is derived from perfluoroalkyl, perfluoroether or perfluoropolyether and a predetermined functional group containing hetero atoms other than C; H or F by which at least one of the fluorine atom is substituted at one or both ends thereof, or a mixture of a plurality of the different materials.
(5) The rolling bearing as described in (4), wherein the predetermined functional group is selected from the group consisting of a carboxyl group, an isocyanate group, an alcoholic hydroxyl group, and an ester group.
(6) The rolling bearing as described in (5), wherein a fluorine derivative of the rust preventive is represented by the following formula (1): 
xe2x80x83wherein p1 and q1 each represents an integer.
(7) The rolling bearing as described in (5), wherein a fluorine derivative of the rust preventive is represented by the following formula (3): 
xe2x80x83wherein p3 and q3 each represents an integer.
(8) The rolling bearing as described in (3), wherein the fluorine-based diluent comprises a low molecular material in an amount of not greater than a predetermined value.
(9) The rolling bearing as described in (8), wherein the diluent has from 4 to 30 carbon atoms and a molecular weight of not greater than 1,700.
(10) The rolling bearing as described in (8), wherein the diluent is a lubricant, solvent or a hydrochlorofluorocarbon (HCFC) alternative comprising a molecular structure comprising its main chain substituted by fluorine, which is selected from the group consisting of perfluoroalkyl, perfluoroether and perfluoropolyether.
(11) The rolling bearing as described in (8), wherein the diluent is represented by the following formula (2): 
xe2x80x83wherein P2 and q2 each represents an integer.
(12) The rolling bearing as described in (1), wherein the bearing comprises a seal plate or a shield plate and an amount of the lubricant to be packed is adjusted such that it accounts from 10% to 50% by volume of the space in the bearing.
(13) The rolling bearing as described in (12), wherein after the lubricant has been packed into the interior of the bearing, the rolling bearing is allowed to run in, and an oil-repellent rust preventive diluted with a diluent is applied to the outer surface of the outer ring and the inner surface of the inner ring.
(14) The rolling bearing as described in (13), wherein the conditions for the running-in operation comprises a period of time of from 3 seconds to 5 minutes and the rotational speed of the rolling bearing of from 300 minxe2x88x921 to 10,000 minxe2x88x921.
(15) The rolling bearing as described in (2), wherein the resin material comprises at least a polycarbonate, a polyacetal, an acrylonitrile-butadiene-styrene copolymer, a polystyrene, a polyphenylene oxide, and a modified polyphenylene oxide.
(16) A bearing apparatus which comprises an inner ring fitted onto a shaft, an outer ring fitted in the housing, a plurality of rolling elements provided interposed between the inner ring and the outer ring and a lubricant packed thereinside and which is mounted between the shaft and the housing, wherein a rust preventive film comprising an oil-repellent material is formed on at least the outer surface of the outer ring and the inner surface of the inner ring.
(17) The bearing apparatus as described in (16), wherein at least one of the shaft and housing is formed by a resin material and the resin material comprises at least a polycarbonate, an acrylonitrile-butadiene-styrene copolymer, a polystyrene, a polyphenylene oxide, and a modified polyphenylene oxide.
(18) The bearing apparatus as described in (16), wherein the bearing apparatus is used in office appliances and information apparatus.
The rolling bearing according to the invention comprises an inner ring fitted onto a shaft, an outer ring fitted in the housing, a plurality of rolling elements provided interposed between the inner ring and the outer ring and a lubricant packed thereinside and is mounted between the shaft and the housing, which is characterized in that a rust preventive film comprising an oil-repellent material is formed on at least the outer surface of the outer ring and the inner surface of the inner ring.
In accordance with the foregoing constitution, a rust preventive film made of an oil-repellent material is formed at least on the outer surface of the outer ring and the inner surface of the inner ring, making it possible to secure a desired rustproofness without causing the deterioration of resin strength even if a resin material having a low crystallinity is used to form the housing or the shaft.
A rust preventive is normally used in the form of solution in a diluent. The diluent is preferably compatible with the rust preventive. From this standpoint of view, as both the rust preventive and diluent there are preferably used fluorine-based chemicals. Further, in order to secure both desired rustproofness and mountability, the rust preventive is preferably contained in the diluent in an amount of from 0.5% to 10% by weight.
In some detail, the rolling bearing of the invention is also preferably characterized in that the rust preventive layer is obtained by applying a rust preventive solution having from 0.5% to 10% by weight of a fluorine-based rust preventive dissolved in a fluorine-based diluent.
Moreover, in order to prevent the diluent from remaining on the surface of the bearing to leave stickiness, the diluent preferably is made of a low molecular material (e.g., material having a molecular weight of not greater than 1,700) in an amount of not greater than a predetermined value.
In other words, the present invention is also preferably characterized in that the fluorine-based diluent is made of a low molecular material in an amount of not greater than a predetermined value.
Further, the rust preventive film of the invention has a low affinity for resin materials and shows low compatibility with resin materials containing a hydrophilic group and thus can provide a desired rustproofness while causing no deterioration of strength of resin materials having a good crystallinity such as polycarbonate (hereinafter referred to as xe2x80x9cPCxe2x80x9d) and polyacetal (hereinafter referred to as xe2x80x9cPOMxe2x80x9d) as well as resin materials which are considered to have a low crystallinity such as acrylonitrile-butadiene-styrene copolymer (hereinafter referred to as xe2x80x9cABSxe2x80x9d), polybutylene terephthalate (hereinafter referred to as xe2x80x9cPBTxe2x80x9d) polystyrene (hereinafter referred to as xe2x80x9cPSxe2x80x9d), polyphenylene oxide (hereinafter referred to as xe2x80x9cPPOxe2x80x9d) and modified PPO.
In other words, the present invention is also preferably characterized in that the resin material comprises at least one of PC, POM, ABS, PS, PPO, and modified PPO.